In silo bottom unloaders of my previous developments, such as U.S. Pat. No. 3,817,409, the disclosure of which I herein incorporate by reference, I have utilized an auger that sweeps across the floor of a silo, in its advancing movement, and which also rotates on its own axis, in response to a drive that is generally centrally located with respect to a center dischargeway or passageway of a silo, at the bottom thereof. In the past, both the traversing motion and the rotational motion for driving the auger have been hydraulic. While offering many operational benefits, substantially complete hydraulic drive systems have come to be expensive, and in many instances prohibitively expensive. In my previous systems, the auger advance has been discontinued upon the auger meeting excess silage resistance. Such discontinuance has been by means of hydraulics.